Field of the Invention
The present invention relates to wireless communications.
Related Art
3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) that is an advancement of UMTS (Universal Mobile Telecommunication System) is being introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonal frequency division multiple access) is used for downlink, and SC-FDMA (single carrier-frequency division multiple access) is used for uplink.
Such LTE may be generally divided into a frequency division duplex (FDD) type and a time division duplex (TDD) type.
As set forth in 3GPP TS 36.211 V10.4.0, the physical channels in 3GPP LTE may be classified into data channels such as PDSCH (physical downlink shared channel) and PUSCH (physical uplink shared channel) and control channels such as PDCCH (physical downlink control channel), PCFICH (physical control format indicator channel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH (physical uplink control channel).
Meanwhile, data is easily distorted or changed while being transmitted through a radio channel. Therefore, a reference signal is needed to demodulate such transmission information without error. A reference signal is a signal known in advance between a transmitter and a receiver and is transmitted along with transmission information. Since transmission information transmitted from a transmitter experiences a corresponding channel in each transmitting antenna or layer, a reference signal may be allocated for each transmitting antenna or layer. A reference signal for each transmitting antenna or layer may be distinguished using a resource, such as time, a frequency, and a code.
However, when a user equipment (UE) located in a fast-moving environment or an environment with a poor channel state receives data based on only a conventionally defined reference signal, the UE has a limitation of being unable to exhibit proper data receiving performance due to deteriorated channel estimation. Therefore, required is a channel estimation solution for a fast-moving environment or an environment with a poor channel state.